Various attempts have been made in the prior art to extend a single point-like optical trap into lines, curves and three dimensional shapes, but serious deficiencies are inherent in all such efforts. For example, line tweezers have been implemented with a cylindrical lens or its holographic equivalent. A line formed with a cylindrical lens is degraded by severe astigmatism, however, and therefore cannot trap objects in three dimensions. A cylindrical lens also cannot produce more general structures, only linear extended traps. Line traps also have been formed with pairs of cylindrical lenses arranged in a Keplerian telescope. Although such line traps can be free from astigmatism, their shape is fixed, and their intensity and phase profiles cannot be altered. Such line traps also are incompatible with the holographic optical trapping technique, and therefore cannot be integrated with the variety of trapping capabilities made possible by holographic projection. In another prior art methodology extended optical traps have been created by time sharing or scanning of optical traps. This method suffers from various disadvantages described in detail hereinafter.
In yet another prior art methodology extended optical traps can be projected by conventional holographic techniques. This approach does not allow for general three dimensional structures for the projected line and suffers from projection deficiencies, such as optical speckle. Further disadvantages will be described hereinafter as part of the description of this invention, thus demonstrating the substantial advantages over the prior art.